Packet switched radio telecommunication system supporting hard handover and method for hard handover

ABSTRACT

A packet switched radio telecommunication system supporting hard handover adapts Always_on technology to a link between a target packet data serving node (PDSN) and a support PDSN. The support PDSN assigns a temporary IP address to a mobile terminal in its service area, and transmits handover data and the mobile terminal&#39;s temporary IP address to the target PDSN via a direct link when the mobile terminal leaves the service area. The target PDSN, upon receiving a registration request for the temporary IP address from the mobile terminal moved to its service area, temporarily registers the temporary IP address in an IP pool. The target PDSN receives down-link frame data for the mobile terminal at the temporarily registered IP address from the support PDSN via the direct link. A new temporary IP address is assigned by the target PDSN when data transmission/reception is complete to the mobile terminal.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.11/690,330, filed on Mar. 23, 2007, and claims priority from and thebenefit of Korean Patent Application No. 10-2006-0028664, filed on Mar.29, 2006, which are both hereby incorporated by reference for allpurposes as if fully set forth herein.

BACKGROUND

1. Field

The present invention relates to a packet switched radiotelecommunication system supporting hard handover and a method for hardhandover, and more particularly to a packet switched radiotelecommunication system supporting mobile IP hard handover without datacorruption or data loss, and a method for hard handover.

2. Discussion of the Background

Mobile Internet Protocol (IP) is a standard IP that incorporatesmobility of devices connected to the internet. Under Mobile IP, an IPaddress is allocated to a mobile terminal when a mobile terminal roamsand temporarily gains access to the internet via a fixed network otherthan the mobile terminal's home network.

FIG. 1 is a block diagram of a network of a conventional packet switchedradio telecommunication system. Mobile IP will now be described indetail with reference to FIG. 1.

Upon initial subscription, a mobile terminal (MS) 101 is connected tothe Internet 106 via its home network area and receives an inherent IPaddress from its home agent (HA) 108. However, when the MS moves fromits home network area to a foreign network area, the MS 101 is assigneda care-of address (CoA) corresponding to an IP address of the foreignagent (FA) 105 in the foreign network area and is assigned a temporaryIP address from the FA 105. Then, a server 107 transmits data to the HA108 using the inherent IP address of the MS 101, even if the MS 101 hasmoved outside of its home network. The HA 108 receives data intended forthe MS 101, encapsulates the data, and transmits the encapsulated datato the CoA corresponding to the IP address of the FA 105 in the foreignnetwork area. The FA 105 then transmits data to the MS 101 using to thetemporary IP address. Thus, data transmitted by the server 107 to the MS101 is routed through the HA 108 and the FA 105 in the foreign networkarea.

In the conventional mobile IP structure described above, when the MS 101carries out handover, the MS 101 first transmits a handover request tothe HA 108 via a support base station controller (BSC) 102, which may becombined with a packet control function (PCF), and a support packet dataserving node (PDSN) 103. Further, when a target FA 105 in the foreignnetwork area to which the MS 101 is moving is connected to a target PDSN105 and a target BSC/PCF 104, the MS 101 disconnects a link set to thesupport BSC 102 and the support PDSN 103, sets a new link to the targetPSDN/FA 105, and is assigned with a temporary IP address from the targetFA 105. Thus, data transmitted from the server 107 is routed by the HA108 to the MS 101 at the temporary IP address provided by the target FA105.

The above-mentioned prior handover method has a problem in that when aMS 101 is hard handed over from a previous channel in the home networkarea to a new channel in the foreign network area, the connection to thehome network area channel is broken before the connection to the foreignnetwork area channel occurs. Accordingly, up-link and down-link pathsare interrupted with respect to radio interface, and frame loss mayresult.

Korean Patent Application Publication No. 10-2001-0062319 discloses ahard handover method in which a direct link is established between thesupport PDSN 103 and the target PDSN 105, thereby causing a shorterdisconnection with the MS 101 during the hard handover.

More specifically, a target PDSN 105 requests the support PDSN 103 for atemporary direct link. Then, when an up-link frame is transmitted froman MS 101 to a support PDSN 103 after the target PDSN 105 requests atemporary direct link with the support PDSN 103, the support PDSN 103transmits the up-link frame from the MS 101 to the target PDSN 105 viathe temporary direct link. At the same time, the support PDSN 103transmits the up-link frame to a core network including the Internet106. Then, the core network concurrently transmits down-link frames toboth the target PDSN 105 and the support PDSN 103. The target PDSN 105determines a handover completion time and transmits a handover commandsignal to the support PDSN 103 via the core network.

However, with Korean Patent Application Publication No. 10-2001-0062319,there may be delays associated with requesting and setting a temporarydirect link between the support PDSN 103 and the target PDSN 105.Further, there may be delays associated with requesting the core networkfor handover and receiving a corresponding response. Because the requestpasses through the core network including the Internet 106, the delaytime may be much greater. Furthermore, a network load is doubled sincedata is transmitted from the core network to both the target PDSN 105and the support PDSN 103 until handover is complete.

SUMMARY

The present invention provides a packet switched radio telecommunicationsystem supporting hard handover without data transmission delay and datacorruption or loss and a method for hard handover.

Additional features of the invention will be set forth as follows, andin part will be apparent from the description, or may be learned bypractice of the invention.

The present invention discloses a packet switched radiotelecommunication system including a support packet data serving node(PDSN) to assign a temporary Internet Protocol (IP) address to a mobileterminal in its service area, to maintain a direct link to a neighboringPDSN, and to transmit handover data and the temporary IP address to theneighboring PDSN via the direct link, and a target PDSN to register thetemporary IP address in an IP pool in response to a request from themobile terminal moved into a service area of the target PDSN. Further,the target PDSN receives down-link frame data from the support PDSN viathe direct link, the down-link frame data being transmitted to themobile terminal at the temporary IP address, and the neighboring PDSN isthe target PDSN.

The present invention also discloses a method for handing over a mobileterminal from a support packet data serving node (PDSN) to a targetPDSN. The method includes assigning a temporary IP address to the mobileterminal in a service area of the support PDSN, configuring a directlink between the support PDSN and the target PDSN and maintaining aprotocol configuration, transmitting handover data and a temporary IPaddress of the mobile terminal from the support PDSN to the target PDSNvia the direct link, requesting registration of the temporary IP addressfrom the target PDSN, and registering the temporary IP address of themobile terminal in an IP pool of the target PDSN.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention, andtogether with the description serve to explain the principles of theinvention.

FIG. 1 is a block diagram of a network of a conventional packet switchedradio telecommunication system.

FIG. 2 is a block diagram of a network of a packet switched radiotelecommunication system according to an exemplary embodiment of thepresent invention.

FIG. 3 is a flow chart illustrating a method for hard handover in thepacket switched radio telecommunication system according to an exemplaryembodiment of the present invention.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

The invention is described more fully hereinafter with reference to theaccompanying drawings, in which embodiments of the invention are shown.This invention may, however, be embodied in many different forms andshould not be construed as limited to the embodiments set forth herein.Rather, these embodiments are provided so that this disclosure isthorough, and will fully convey the scope of the invention to thoseskilled in the art. In the drawings, the size and relative sizes oflayers and regions may be exaggerated for clarity Like referencenumerals in the drawings denote like elements.

It will be understood that when an element is referred to as being“connected to” another element, it can be directly connected to theother element, or intervening elements may be present. In contrast, whenan element is referred to as being “directly connected to” anotherelement, there are no intervening elements present.

Always_on technology included in the present invention will now beexplained briefly prior to describing the exemplary embodiments.

Always_on technology is technology that always maintains a Point toPoint Protocol (PPP) connection of a data link between a mobile terminaland a PDSN/FA. If the mobile terminal is powered on and Always_ontechnology is activated, the PPP configuration between the mobileterminal and a network is maintained. Maintaining the PPP configurationequates to maintaining an authentication process and the networkprotocol configuration between end-to-end nodes even without datatraffic. Thus, while maintaining the PPP configuration, data can bedirectly received and/or transmitted between the mobile terminal andPDSN/FA without a separate PPP connection process.

FIG. 2 is a block diagram of a network of a packet switched radiotelecommunication system according to an exemplary embodiment of thepresent invention.

The present invention adapts the Always_on technology to a link 208 abetween a target PDSN 205 and a support PDSN 203 as illustrated in FIG.2. That is, authentication or a network protocol for an MS 201 connectedto the support PDSN 203 is previously configured and then maintained.Thus, when an MS 201 is handed over from the support PDSN 203 to thetarget PDSN 205, the support PDSN 203 can directly transmit informationof the MS 201 hand over to the target PDSN 205. In addition, the supportPDSN 203 can transmit a down-link frame received from the server 207 tothe target PDSN 205.

In FIG. 2, the support PDSN 203 has an IP pool 209, and the target PDSN205 has an IP pool 210. In general, an IP pool such as IP pool 210includes temporary IP addresses that may be assigned to a roaming MS 201by a target PDSN/FA 205 via target BSC/PCF 204. A target PDSN/FA 205temporarily assigns one of temporary IP addresses in the IP pool 210 tothe MS 201 that configures a connection to the target PDSN/FA 205. TheIP pool is exemplified as follows:

IP pool 210 in target PDSN: (3.0.0.1), (3.0.0.2), (3.0.0.3), (3.0.0.4),. . .

IP pool 209 in support PDSN: (2.0.0.1), (2.0.0.2), (2.0.0.3), (2.0.0.4),. . .

However, according to the present invention, the MS 201 is assigned witha temporary IP address from the support PDSN 203 and transmits data tothe server 207 via link 201 a, 202 a, 203 a, and 204 a. If the MS 201 ishanded over to the target PDSN 205, the MS continues to use thetemporary IP address assigned from the support PDSN 203 without beingassigned with a temporary IP address from the target PDSN 205.

For example, an inherent IP address of the MS 201 registered in its HA208 may be 1.0.0.1, and a temporary IP address assigned from the supportPDSN 203 is 2.0.0.1.

Data intended for the MS 201 is transmitted from the server 207 to theInternet 206 via a link 204 a and then to the HA 208 via a link 205 a.The data is encapsulated at the HA 208. The encapsulated data istransmitted from the HA 208 to the Internet 206 via link 205 a, and thento the current support PDSN 203 via the link 203 a. The encapsulateddata transmitted to the support PDSN 203 is transmitted to the MS 201having the temporary IP address 2.0.0.1 via a support BSC/PCF 202. Totransmit data, the MS 201 transmits data to the server 207 via link 201a, link 202 a, link 203 a, and the link 204 a without passing throughthe HA 208.

When the MS 201 carries out handover, the support PDSN 203 transmitshandover data to the target PDSN 205 via the direct link 208 a withouttransmitting the same to the core network, which includes the Internet206 and the server 207. Herein, the support PDSN 203 transmits thetemporary IP address 2.0.0.1 assigned to the MS 201 to the target PDSN205.

Then, the MS 201 carrying out handover requests registration of thetemporary IP address 2.0.0.1 from the target PDSN 205 via the targetBSC/PCF 204. When the temporary IP address included in the registrationrequest is identical to the temporary IP address transmitted from thesupport PDSN 203 to the target PDSN 205 via the link 208 a, the targetPDSN 205 temporarily registers the temporary IP address in its IP pool210, and allows the MS 201 to use the temporary IP address continuously.

In addition, down-link frame data transmitted from the server 207 to thesupport PDSN 203 via the HA 208 is transmitted to the target PDSN 205via a link 208 a, and then the down-link frame data transmitted to thetarget PDSN 205 is transmitted to the MS 201 using the temporary IPaddress 2.0.0.1 via link 207 a. The MS 201 being in an activated stateand using the temporary IP address assigned by support PDSN 203 cancarry out handover without data corruption or loss through the aboveprocess.

If the MS 201, which has carried out handover to the target PDSN 205 andstill uses the temporary IP address assigned by the support PDSN 203,enters into a data dormant state, or has completed data transmission,the MS 201 may relinquish the temporary IP address 2.0.0.1 of thesupport PDSN 203 to the support PDSN 203. The MS 201 is then assignedwith a new temporary IP address 3.0.0.1 through a new PPP connection tothe target PDSN 205, and registers a Care-of Address (CoA) of the targetFA 205 in the core network including the HA 208. Then, when the MS 201comes out of the dormant state, or receives/transmits data again, theserver 207 transmits the data to the target PDSN 205 at the CoA via theHA 208, link 205 a, and link 206 a, and then the target PDSN 205transmits the data to the MS 201 assigned with the temporary IP address3.0.0.1.

FIG. 3 is a flow chart illustrating a method for hard handover in thepacket switched radio telecommunication system according to an exemplaryembodiment of the present invention.

As illustrated in FIG. 3 a direct link is configured between a supportPDSN and a target PDSN using Always_on technology at step S301. That is,the target PDSN configures the authentication for the MS having beenconnected to the support PDSN or configures a network protocol, andmaintains the same.

Then, if the MS connected to the support PDSN carries out handover, thesupport PDSN transmits to the target PDSN 205 the handover data of theMS and the temporary IP address data assigned to the MS by the supportPDSN at step S302.

Next, the MS requests the target PDSN for registration of the currentlyused temporary IP address assigned by the support PDSN via the targetBSC at step S303.

The target PDSN compares the temporary IP address in the registrationrequest from the MS with the temporary IP address transmitted by thesupport PDSN via the direct link at step S304.

If the temporary IP address in the registration request from the MS isidentical to the temporary IP address transmitted by the support PDSN,the target PDSN temporarily registers the temporary IP address in its IPpool at step S305.

Then, down-link frame data transmitted from the internet server via theHA to the support PDSN is transmitted to the target PDSN via the directlink at step S306.

The target PDSN receives the down-link frame data transmitted via thedirect link and transmits the down-link frame data to the MS carryingout handover via the target BSC at step S307.

Meanwhile, if the MS is in a data dormant state, or has completed datatransmission, the MS gives back the temporary IP address assigned by thesupport PDSN to the support PDSN at step S308.

Then, the MS is assigned a new temporary IP address for a new PPPconnection by the target PDSN, and registers the CoA of the changed FAin the core network including the HA at step S309.

Then, if the MS comes out of the dormant state, or receives/transmitsdata again, the internet server transmits the down-link frame data tothe target PDSN at the CoA via the HA at step S310

The target PDSN transmits the down-link frame data to the MS assigned tothe new temporary IP address at step S311.

The above-mentioned method of the present invention may be embodied intoa program so that it is stored in a recording medium, such as CD-ROM,RAM, floppy disc, hard disc, magneto-optical disc, in a form readable bya computer.

As set forth before, according to the present invention, a direct linkis configured between the target PDSN and the support PDSN, therebyreducing a time delay in requesting handover. The handover is performedwithout informing the core network of the handover state of the MS,thereby reducing a delay occurring due to the core network. Moreover, inperforming the handover by the MS, the IP re-configuration is not neededso that data corruption or loss may not occur.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present inventionwithout departing from the spirit or scope of the invention. Thus it isintended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

1. A method for handing over a mobile device from a first node to a second node, comprising: transmitting handover data and a first temporary Internet Protocol (IP) address assigned to the mobile device to the second node via a direct link configured with the second node while a protocol configuration is maintained; transmitting down-link frame data for the mobile device to the second node via the direct link; and requesting registration of a second temporary IP address to the second node by the mobile device, wherein the second node compares the first temporary IP address with the second temporary IP address, and registers the first temporary IP address in an IP pool if the first temporary IP address and the second temporary IP address.
 2. The method of claim 1, wherein the down-link frame data for the mobile device is transmitted from a core network to the first node, the core network comprising a home agent of the mobile terminal.
 3. A method for handing over a mobile device to from a first node to a second node, comprising: receiving handover data and a first temporary Internet Protocol (IP) address assigned to the mobile device from the second node via a direct link configured with the second node while a protocol configuration is maintained; receiving a request for registration of a second temporary IP address by the mobile device; registering the first temporary IP address if the first temporary IP address received from the second node is identical to the second temporary IP address received from the mobile terminal; receiving down-link frame data transmitted from a core network via the direct link; and transmitting the down-link frame data to the mobile terminal.
 4. The method of claim 3, wherein the first temporary IP address is registered in an IP pool of the second node.
 5. The method of claim 3, wherein the mobile device gives back the first temporary IP address if data transmission or reception is complete or if the mobile device enters a dormant state.
 6. The method of claim 5, further comprising: assigning the mobile device with a new temporary IP address through a Point to Point Protocol (PPP) connection; and registering the new temporary IP address in the core network.
 7. The method of claim 3, wherein the core network comprises a home agent of the mobile terminal.
 8. The method of claim 6, wherein the new temporary IP address corresponds to an IP address in an IP pool. 